Effects Of Imazethapyr On Soil Microorganism, Enzyme Activity And Isolation Of Imazethapyr Degrading Fungi

Imazethapyr, developed by the American Cyanamid Company is one of the imidazolinone herbicides. It is one of the most popular herbicides in soybean feld with high efficacy, low cost and good safety. Imazethapyr's degradation rate is very slow. Large amounts of imazethapyr were used in field year after year, which caused the soil contamination and injuried to subsequent crops. The effects of imazethapyr on soil culturable microorganisms and soil enzyme activity were measured to evaluate soil environment and quality. The fungi which can degrade imazethapyr was also isolated and it's characteristics of growth and degradation was studied elementally. The results showed as followings.1. Effects of imazethapyr on soil culturable microorganisms densities were investigated by the dilution plate method. There were no significant changes in the soil culturable bacteria densities at the recommended rate (0.1μg/g) of imazethapyr, but the densities of culturable fungi and actinomycetes increased in the same treatment. All of the soil culturable bacteria, fungi and actinomycetes'densities increased at 10-fold and 100-fold recommended rates of imazethapyr.2. Effects of imazethapyr on the soil catalase, urease and protease's activity were measured by potassium permanganate titrimetri, phenol sodium colorimetry and Folin colorimetry methods respectively. There were no significant changes on the soil catalase, urease and protease's activity at the recommended rate in 28 days after application. The soil catalase, urease and protease's activity increased at 10-fold and 100-fold higher rates in 28 days after herbicide application.3. Two methods for the determination of imazethapyr residues in medium were estimated based on bioassay and instrument analysis. A bioassay for imazethapyr residues in water and agar was determined by filter paper and agar method with cole, the detection range of imazethapyr was between 0.005 and 1 mg/L in water, 0.01 and 1 mg/L in agar, separately. The other bioassay for imazethapyr residues was estimated using corn, which detection range was between 0.02 and 1 mg/L in agar. Solid phase extraction and ultra-performance liquid chromatography-mass spectrometry method was estimated to determine imazethapyr between 0.01 and 1 mg/L in water.4. 21 bacteria and 9 fungi were isolated from the soil by enrichment method. The one of the fungi , 114-G, can degrade imazethapyr 34.34% in 3 days in inorganic salt medium; 114-G is identified as Fusarium solani.5. The characteristics of 114-G's growth and degradation were studied. The optimum growth conditions of the 114-G in potato sucrose medium were the optimum temperature 30℃, the optimum original pH 8 and the optimum aeration rate 68% (volume 80 mL medium in 250 mL bottle); The optimum growth conditions of the 114-G in inorganic salt medium (containing imazethapyr 50 mg/L) were the optimum temperature 30℃, the optimum original pH 9 and the optimum aeration rate 68% (volume 80 mL medium in 250 mL bottle). The optimum degradation conditions of the 114-G in inorganic salt medium (containing imazethapyr 50 mg/L) were the optimum temperature 30℃, the optimum original pH 9, the optimum aeration rate 68% (volume 80 mL medium in 250 mL bottle) and the optomum inoculum size 10%. These results provided the data for the effects of imazethapyr on the soil ecological environment and a method for the bioremediation of the soil contaminated by imazethapyr.